1. Field of the Invention
This invention relates to a magnetic recording medium in which a ferromagnetic film comprising essentially of Co, Ni, Fe, or an alloy thereof is used as a magnetic layer.
2. Statement of the Related Art
In the field of the magnetic recording, it is incumbent to improve the recording density, such that it is contemplated to employ the magnetic recording medium employing the ferromagnetic film as the magnetic layer (hereafter referred to as the thin film type magnetic recording medium), instead of the conventional coating type magnetic recording medium.
The thin film type magnetic recording medium is formed by processing the ferromagnetic metal material, such as Co-Ni, on the substrate into a thin film by physical vapour deposition such as the vacuum evaporation method to form a magnetic layer. Since the high molecular binder is not used as in the case of the coating type magnetic recording medium, high residual magnetic flux density is obtained, while the high output and superior response to short wavelength characteristics can be obtained since an extremely thin film thickness of the ferromagnetic film may be obtained.
It is noted that, in the above described thin film type magnetic recording medium, it is difficult to procure coercive force by simply evaporating the ferromagnetic metal material, such as Co-Ni, on the non-magnetic substrate, so that it is customary to form the ferro-magnetic film by oblique evaporation, however, the lower evaporation efficiency is not desirable in this case in regard to productivity.
In the case of the disk-shaped magnetic recording medium extensively used as the recording medium for computers, problems are presented in orientation characteristics obtained by the aforementioned oblique evaporation. These orientation characteristics are acceptable to some extent with an elongated magnetic recording medium such as the magnetic tape, however, such orientation characteristics in the disk-shaped ferromagnetic recording medium result in increased modulation in the envelope waveform of the playback output.
The present Applicant has proposed a magnetic recording medium in the Japanese Laid-Open Patent Publication No. 204831/1986 wherein a low melting metal (non-magnetic metal) is deposited previously as a film and the ferromagnetic metal material is deposited as a film from a substantially perpendicular direction by vacuum evaporation. This magnetic recording medium exhibits superior characteristics in evaporation efficiency and orientation characteristics as well as the required coercive force.
Needless to say, higher rectangular characteristics of the hysteresis loop is required of the magnetic recording medium employed in the field of the digital magnetic recording technology employed in, for example, data recording. This means that the distribution of the coercive force is uniform. It can be easily be premeditated that the majority of endeavors for evolving the magnetic recording medium has been expended in improving these characteristics.
In this light, the aforementioned magnetic recording medium has much to be desired and a further improvement is desirable.